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          <h1 class="post-title" itemprop="name headline">Flask构建可扩展的RESTful-API-6--模型对象的序列化</h1>
        

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        <h1 id="6-模型对象的序列化"><a href="#6-模型对象的序列化" class="headerlink" title="6. 模型对象的序列化"></a>6. 模型对象的序列化</h1><h3 id="1-理解序列化时的default函数"><a href="#1-理解序列化时的default函数" class="headerlink" title="1.理解序列化时的default函数"></a>1.理解序列化时的default函数</h3><p>我们最想做的一件事情，就是在视图函数中，读取出模型之后，还要把他的属性读出来，转换成一个字典。我们想直接<code>jsonfiy(user)</code></p>
<p>现在jsonfiy并不能直接序列化对象，所以我们的目标就是必须想办法让jsonfiy直接序列化对象。</p>
<p>jsonfiy在序列化对象的时候，如果不知道如何序列化当前传进来的参数，就会去调用JSONEncoder类的default函数。<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line">def default(self, o):</span><br><span class="line">&quot;&quot;&quot;Implement this method in a subclass such that it returns a</span><br><span class="line">serializable object for ``o``, or calls the base implementation (to</span><br><span class="line">raise a :exc:`TypeError`).</span><br><span class="line"></span><br><span class="line">For example, to support arbitrary iterators, you could implement</span><br><span class="line">default like this::</span><br><span class="line"></span><br><span class="line">def default(self, o):</span><br><span class="line">    try:</span><br><span class="line">        iterable = iter(o)</span><br><span class="line">    except TypeError:</span><br><span class="line">        pass</span><br><span class="line">    else:</span><br><span class="line">        return list(iterable)</span><br><span class="line">    return JSONEncoder.default(self, o)</span><br><span class="line">&quot;&quot;&quot;</span><br><span class="line">    if isinstance(o, datetime):</span><br><span class="line">        return http_date(o.utctimetuple())</span><br><span class="line">    if isinstance(o, date):</span><br><span class="line">        return http_date(o.timetuple())</span><br><span class="line">    if isinstance(o, uuid.UUID):</span><br><span class="line">        return str(o)</span><br><span class="line">    if hasattr(o, &apos;__html__&apos;):</span><br><span class="line">        return text_type(o.__html__())</span><br><span class="line">    return _json.JSONEncoder.default(self, o)</span><br></pre></td></tr></table></figure></p>
<p>目前的default是没有提供对对象的序列化的，所以我们这里最关键的就是要重写default方法。在重写的过程中实现对对象的序列化就可以了</p>
<h3 id="2-不完美的对象转字典"><a href="#2-不完美的对象转字典" class="headerlink" title="2.不完美的对象转字典"></a>2.不完美的对象转字典</h3><p>我们首先要做到的就是让Flask可以调用到我们自己定义的default函数。要做到这一点，我们需要继承JSONEncoder，然后重写defualt方法，然后继承Flask，在子类里，替换掉Flask原有的json_encoder对象。然后，是实例化Flask核心对象的时候，使用我们的子类进行实例化<br>app__init__.py<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br></pre></td><td class="code"><pre><span class="line">from flask import Flask as _Flask</span><br><span class="line"></span><br><span class="line">from flask.json import JSONEncoder as _JSONEncoder</span><br><span class="line"></span><br><span class="line">class JSONEncoder(_JSONEncoder):</span><br><span class="line">	def default(self,o):</span><br><span class="line">		# return o.__dict__  # 内置方法，将对象转化为字典  # 缺点是只能转换实例变量，不能将类变量也转换成字典</span><br><span class="line">    return dict(o)</span><br><span class="line"></span><br><span class="line">class Flask(_Flask):  # 定义自己的Flask核心对象，继承原来的Flask核心对象</span><br><span class="line">	json_encoder = JSONEncoder # 替换原本的JSONEncoder</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 将Blueprint注册到flask核心对象上,并传入一个前缀&apos;/v1&apos;</span><br><span class="line">def register_blueprints(app):</span><br><span class="line">    # from app.api.v1.user import user</span><br><span class="line">    # from app.api.v1.book import book</span><br><span class="line">    # app.register_blueprint(user)</span><br><span class="line">    # app.register_blueprint(book)</span><br><span class="line">    from app.api.v1 import create_blueprint_v1</span><br><span class="line">    app.register_blueprint(create_blueprint_v1(), url_prefix = &apos;/v1&apos;)</span><br><span class="line"></span><br><span class="line">def registe_plugin(app):  # 插件的注册</span><br><span class="line">    from app.models.base import db</span><br><span class="line">    db.init_app(app)</span><br><span class="line"></span><br><span class="line">    with app.app_context():  # 上下文环境 把app推入到上下文栈中 才能使用create_all</span><br><span class="line">        db.create_all()  # 来创建所有数据库，数据表</span><br><span class="line"></span><br><span class="line">def create_app():</span><br><span class="line">    app = Flask(__name__)   # 实例化flask核心对象</span><br><span class="line">    app.config.from_object(&apos;app.config.secure&apos;)  # 读取配置文件下的secure</span><br><span class="line">    app.config.from_object(&apos;app.config.setting&apos;) # 读取配置文件下的setting</span><br><span class="line"></span><br><span class="line">    register_blueprints(app)    # 注册蓝图到核心对象上</span><br><span class="line">    registe_plugin(app)  # 最后调用 registe_plugin</span><br><span class="line"></span><br><span class="line">    return app</span><br></pre></td></tr></table></figure></p>
<p>上面的写法o.<strong>dict</strong>只能转换实例变量，不能将类变量也转换成字典。</p>
<h3 id="3-深入理解dict机制"><a href="#3-深入理解dict机制" class="headerlink" title="3.深入理解dict机制"></a>3.深入理解dict机制</h3><p>在Python中创建一个dict有很多种方式:</p>
<ol>
<li><p>直接定义一个字典</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">r = &#123;</span><br><span class="line">&apos;name&apos;: &apos;gwf&apos;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p>使用dict函数</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">r = dict(name=&apos;gwf&apos;)</span><br></pre></td></tr></table></figure>
</li>
<li><p>将一个对象传入dict函数 值得研究的是这第三种方法，当将一个对象传入dict函数的时候，他会去调用keys函数</p>
</li>
</ol>
<p><img src="http://upload-images.jianshu.io/upload_images/14597179-b9ec37217f768ff1?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="image"> </p>
<p>keys 方法的目的就是为了拿到字典里所有的键，至于说这些键有那么，完全有我们自己来定义。keys 返回的必须是一个元组或者列表来声明要序列化的键。</p>
<p>而dict会以中括号的形式来拿到对应的值，如o[“name”]，但是默认是不能这么访问的，我们需要编写<strong>getitem</strong>函数<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line">r = &#123;&apos;name&apos;: &apos;weilai&apos;&#125;  # 直接定义一个字典</span><br><span class="line"></span><br><span class="line">r = dict(name= &apos;weilai&apos;) # 使用dict函数</span><br><span class="line"></span><br><span class="line">class Wei():</span><br><span class="line">    name = &apos;weilai&apos;</span><br><span class="line">    age = &apos;age&apos;</span><br><span class="line"></span><br><span class="line">    def __init__(self):</span><br><span class="line">        self.gender = &apos;male&apos;</span><br><span class="line"></span><br><span class="line">    def keys(self):   </span><br><span class="line">        return (&apos;name&apos;,&apos;age&apos;,&apos;gender&apos;)  #  取到 key ,  做到自定义key </span><br><span class="line">        # # return (&apos;name&apos;,)  # 一个元素的元组</span><br><span class="line">        # return [&apos;name&apos;]  # return 序列类型的都可以</span><br><span class="line"></span><br><span class="line">    def __getitem__(self,item):  </span><br><span class="line">        return getattr(self,item)   # 取到 key对应的value</span><br><span class="line"></span><br><span class="line">o = Wei()</span><br><span class="line">print(dict(o))   # &#123;&apos;name&apos;: &apos;weilai&apos;, &apos;age&apos;: &apos;age&apos;, &apos;gender&apos;: &apos;male&apos;&#125;</span><br></pre></td></tr></table></figure></p>
<p>这样我们就成功的讲一个对象转化成了字典的形式，并且无论类变量和实例变量，都可以转化，更加灵活的是，我们可以自己控制，那些变量需要转化，哪些变量不需要转化</p>
<h3 id="4-序列化SQLALChemy模型"><a href="#4-序列化SQLALChemy模型" class="headerlink" title="4.序列化SQLALChemy模型"></a>4.序列化SQLALChemy模型</h3><p>有了之前的基础，我们就知道怎么序列化user对象了，我们只需要在User类中定义keys和getitem方法，然后在default函数中使用dict()函数即可<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">class JSONEncoder(_JSONEncoder):</span><br><span class="line">    def default(self, o):</span><br><span class="line">        return dict(o)</span><br><span class="line"></span><br><span class="line">class Flask(_Flask):</span><br><span class="line">    json_encoder = JSONEncoder</span><br></pre></td></tr></table></figure></p>
<p>models/user.py<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line">class User(Base):</span><br><span class="line">    id = Column(Integer, primary_key=True)</span><br><span class="line">    email = Column(String(50), unique=True, nullable=False)</span><br><span class="line">    auth = Column(SmallInteger, default=1)</span><br><span class="line">    nickname = Column(String(24), nullable=False)</span><br><span class="line">    _password = Column(&apos;password&apos;, String(128))</span><br><span class="line"></span><br><span class="line"># SQLALChemy的实例化是不会调用__init__函数的，要想让他调用就需要</span><br><span class="line"># @orm.reconstructor这个装饰器</span><br><span class="line">    @orm.reconstructor</span><br><span class="line">    def __init__(self):</span><br><span class="line">        self.fields = [&apos;id&apos;, &apos;email&apos;, &apos;nickname&apos;]</span><br><span class="line"></span><br><span class="line">    def keys(self):</span><br><span class="line">	return self.fields</span><br><span class="line"></span><br><span class="line">	# 支持隐藏字段</span><br><span class="line">    def hide(self, *keys):</span><br><span class="line">	[self.fields.remove(key) for key in keys]</span><br><span class="line">	# 支持添加字段</span><br><span class="line">    def append(self, *keys):</span><br><span class="line">	[self.fields.append(key) for key in keys]</span><br></pre></td></tr></table></figure></p>
<h3 id="5-完善序列化"><a href="#5-完善序列化" class="headerlink" title="5.完善序列化"></a>5.完善序列化</h3><p>优化1：每一个模型如果需要序列化，都要有getitem方法，可以放到基类里面去</p>
<p>优化2：default函数，是递归调用的，只要遇到不能序列化的对象，就会调用default函数。所以如果有其他类型，我们需要修改完善我们的default函数</p>
<p>优化3：我们的default函数需要增加容错性<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">class JSONEncoder(_JSONEncoder):</span><br><span class="line">	def default(self,o):</span><br><span class="line">		# return o.__dict__  # 内置方法，将对象转化为字典  # 缺点是只能转换实例变量，不能将类变量也转换成字典</span><br><span class="line">		# return dict(o) # 考虑不全面.o得有上次定义的那两种方法才不会报错</span><br><span class="line"></span><br><span class="line">		if hasattr(o, &apos;keys&apos;) and hasattr(o, &apos;__getitem__&apos;):</span><br><span class="line">			return dict(o)   # 得有这两种方法 才会return dict(o)</span><br><span class="line">		if isinstance(o, date):  # 如果是 时间类型</span><br><span class="line">			return o.strftime(&apos;%Y-%m-%d&apos;)</span><br><span class="line">		raise ServerError()</span><br></pre></td></tr></table></figure></p>
<p>优化4：之前编写的新的Flask类，JsonEncoder类都是不会轻易改变的，放到app.py中。<br>一些其他方法，却是 经常改变的，应该把他们放在init文件中</p>
<h3 id="6-ViewModel对于API有意义吗？"><a href="#6-ViewModel对于API有意义吗？" class="headerlink" title="6.ViewModel对于API有意义吗？"></a>6.ViewModel对于API有意义吗？</h3><p>viewmodel对于API来说，特别是内部开发来说非常有意义</p>
<p>viewmodel是为了我们的视图层，提供个性化的试图模型。SQLALChemy返回的模型是原始模型（格式和数据库中存储的一模一样）。 而前端可能需要我们返回一个意义更加明确的字段。</p>
<p>原始模型是根据数据库来生成的，他的格式是一定的，但是我们在视图层中或者API的返回中，要根据业务去具体的个性化一个个属性的 格式，这就必然存在一个由原始模型向视图模型转换的过程，这个过程最适合的是在View_model中进行一个转换。</p>
<p>我们在视图层写转换的代码，一来会污染视图层的代码，二来会难以复用 并且有的试图模型可能会比较复杂，设计到多个原始模型，这个代码必定会比较复杂，写在视图函数中就会非常不合适</p>
<p>对于完全严格意义上的RESTFul，viewmodel的意义并不大，因为完全资源意义的RESTFul是不考虑业务逻辑的</p>

      
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#6-模型对象的序列化"><span class="nav-number">1.</span> <span class="nav-text">6. 模型对象的序列化</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#1-理解序列化时的default函数"><span class="nav-number">1.0.1.</span> <span class="nav-text">1.理解序列化时的default函数</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#2-不完美的对象转字典"><span class="nav-number">1.0.2.</span> <span class="nav-text">2.不完美的对象转字典</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#3-深入理解dict机制"><span class="nav-number">1.0.3.</span> <span class="nav-text">3.深入理解dict机制</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#4-序列化SQLALChemy模型"><span class="nav-number">1.0.4.</span> <span class="nav-text">4.序列化SQLALChemy模型</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#5-完善序列化"><span class="nav-number">1.0.5.</span> <span class="nav-text">5.完善序列化</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#6-ViewModel对于API有意义吗？"><span class="nav-number">1.0.6.</span> <span class="nav-text">6.ViewModel对于API有意义吗？</span></a></li></ol></li></ol></div>
            

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                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
                    var start = position - 20;
                    var end = position + 80;
                    if(start < 0){
                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
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